The invention relates to a flexible sheet-like material for defining a matrix material feed space in the production of fibre-reinforced plastics material components from composite fibre semi-finished products. The invention also relates to a process for the production of a flexible sheet-like material of this type.
In the production of fibre-reinforced plastics material components, it is known that dry composite fibre semi-finished products, so-called preforms, are initially used which are impregnated with flowable, curable matrix material in the form of resin. The dry composite fibre semi-finished product can be present as woven fabric, as multi-axial non-crimp fabric or as chain-reinforced unidirectional semi-finished product and consists in particular of carbon fibres, glass fibres, aramid fibres, boron fibres or hybrid materials.
A process for the production of fibre-reinforced plastics material components is known as the resin-film-infusion (RFI) process. In this process, a dry carbon fibre woven fabric or non-crimp fabric is deposited in a curing device and covered from outside with a defined amount of resin film. Thereafter, the plastics material component consisting of the carbon fibres and resin is cured under pressure and heat in an autoclave or in another pressure vessel. However, the use of pressure vessels and the complex moulds required for this purpose are very expensive. Furthermore, it is difficult to manage a process of this type in respect of temperature and pressure. Moreover, the available autoclaves restrict the size of the plastics material components to be produced.
To avoid these disadvantages, a process has been developed which is described in DE 100 13 409 C1 and is called “VAP” (Vacuum Assisted Process). This process uses a multi-layer, flexible sheet-like material which defines a matrix feed space in which the semi-finished product is arranged. The sheet-like material consists of a plurality of separate layers which are to be handled independently of one another, namely a membrane which is permeable to gas but impermeable to matrix material, a highly gas-permeable spacer layer and a gas-impermeable film. These layers are successively positioned individually over a flow-promoting layer which is applied onto the semi-finished product. When the region between the film and the membrane is evacuated, thereby causing the build-up of a vacuum, the pressure is also reduced accordingly in the inner matrix feed space through the membrane, as a result of which liquid resin (matrix material) is drawn by suction from an external resin container into the matrix material feed space. In this respect, although the membrane allows gases to escape out of the matrix feed space into the spacer layer and from there to the outside, at the same time it holds back the resin in the matrix material feed space, so that the resin can infiltrate into the semi-finished product.
Although VAP affords considerable advantages over processes which use autoclaves, it suffers from the particular problem that the individual layers of the sheet-like material, namely the membrane, the spacer layer and the gas-impermeable film have to be positioned very precisely and without tension in succession over the semi-finished product. Accordingly, this is time-consuming and, if not performed accurately, can adversely affect the process reliability and can result in non-uniform accumulations in the matrix material.
These problems are avoided by a multi-functional laminate which is described in DE 10 2008 006 261 B3. In this case, a textile layer is laminated onto the membrane, which is permeable to gas but impermeable to matrix material, and furthermore the spacer layer is fixed to the textile layer. The gas-permeable film can either be positioned separately over the spacer layer or firmly joined to the spacer layer and, in the latter case, the film is also a fixed component of the multi-functional laminate. This multi-functional laminate provides significant advantages in respect of management, process accuracy and process reliability. However, with a multi-layer laminate of this type, the desired mechanical material characteristics and the characteristics in respect of gas permeability, matrix material impermeability and temperature resistance of the membrane and of the textile layer often cannot be accurately adjusted in the desired simple manner. The reasons for this are, inter alia, that the characteristics, present before the lamination process, of the membrane on the one hand and of the textile layer on the other can change significantly due to the lamination process and depending on the type, application method and amount of adhesive used between membrane and textile layer during lamination. A further disadvantage is that in these known configurations, the flow front of the resin cannot be observed, because the above-mentioned sheet-like materials are non-transparent.